"Positive" racism is not a positive thing. A positive 'ism' is one that isn't on the surface of things derogatory or obvious, but still contributes to discrimination and prejudice.
A good example of a 'positive ism' would be the concept that women should be protected. While on the surface of things it sounds like a good idea (be a gentleman, etc., etc.), it presupposes that women are unable to take care of themselves and need to be protected, which is obviously neither true nor (ironically) a positive attitude to have.
@An4ximandros: I have no idea what you mean by that.